Electron discharge device



Feb. 18, 1936. H. w. PARKER ELECTRON DISCHARGE DEVICIE Filed April 4, 1934 INVENTOR g W. Parka! B a? ATTORNEY Patented Feb. 18, 1936 ATENTOFFIQE ELECTRON DISCHARGE DEVICE Canada Application April 4,. 1934,Serial No. 718,963

S'CIaims.

My invention pertains to electron discharge de-' vices and relates inparticular to that type of such devices known as thermionic tubes.

Thermionic tubes as universally constructed. 6 employ a control gridlocated between the cathode and the anode. Such constructionnecessitates providing an-anode of considerable surface area in orderthat-the temperature of the anode may. be maintained sufficiently low toensure that the control grid enclosed thereby will not attain atemperature high enough to emit electrons and thereby lower the inputimpedance of the tube.

It is an object of my invention to reduce. the area of the anode andthus simplify and render more economical the construction and at thesametime retain the desirable electrical characteris tics of such tubes andattain new advantageous electrical characteristics.

Another object comprises increasing the energy radiation of the anodethat an effective energy dissipation may be attained.

Another object comprises producing a thermionic tube in which due to thenovel form and psitioning of the control grid with respect to the anodeand cathode, a multiplication-of the amplification factor may beattained.

An additional object comprises producing a thermionic tube in which avariable amplification factor may be attained.

A further object comprises producing a'thermionic tube having a largegrid area whereby the temperature of the grid may be maintainedsufficiently low to eliminate primary electron emisson.

A still further object comprises producing a thermionic tube in' whichthe direct capacitance between the anode and control grid is a minimumwhereby the tube may be effectively used as a short wave oscillator.

I accomplish all of the above noted desirable features and others whichwill be hereinafter pointed out and described by means of a novelconstruction in which the control grid is disposed externally withrespect to the cathode and the anode and is formed with re-entrant orconstricted portions between the cathode and anode whereby both" theanode and the cathode. are partially encircled by the grid.

In the drawing accompanying and forming a part of this specification andin which like reference numbers designate corresponding partsthroughout:

Fig. 1 is a side view of my improved tube with a portion of the envelopebroken away to show the electrodes therein;

Fig. 2 is a side view'of my improved tube with the enclosing envelopebroken away to show an alternative connection of the anodes.

Fig. 3 is a sectional plan view taken-on the line 3-3 of Fig. 2; and

Fig. 4 is a top view of the structure shown in Fig. 1 with the envelopeomitted.

Referring now particularly'to Figs. 1, 3, and 4, the envelope I, whichis preferably of glass or other vitreous material, is provided with astem and press 8 and the usual base 2 containing contact prongs 3, 4, 5,6, and 1. The envelope l and base 2 are preferably provided with a metalcoating 2| sprayed thereon as described in my Patent No. 1,958,953,issued May 15, 1934, for a purpose which will hereinafter be discussed.

The press 8 supports a cathode H, the heater terminals of which areconnected as shown to contact prongs 5 and 6. The cathode may be, asshown, of the indirect heated type or it may be of the filamentary typeeither coated or uncoated. Adjacent the cathode and likewise supportedfrom the press are rod-like anodes l2 and 13. These are electricallyinterconnected by conductor l4 and are connected as shown tocontact'prong 4. A pair of standards 9 and 10, one of which, 9, isconnected to contact prong 3, are supported by the press and serve tosupport the control grid 15 which is shown for the sake of simplicity inthe form of a conductor Wound in helical form on the standards 9 andIll. The electrodes are maintained in their relative positions withrespect to each other by means of I spacers l1 and I8. Preferably thesespacers are constructed of any well-known ceramic adapted to withstandhigh temperature.

There is provided an additional spacer 20 which may be of mica for thepurpose of positioning the upper portion of the electrode assembly inthe envelope I. This spacer 20 is as shown in Fig. 4 provided with acentral aperture to remove the material of the spacer from contact withthe cathode II and the anodes l2 and I3 in order to preventdeterioration of the mica spacer by the high temperature carried bythese electrodes.

The control grid 15 is as shown in Fig. 3 positioned externally withrespect to the anode rods 12 and l3 and the cathode H. The control gridmay be constructed on a mandrel and. is formed with re-entrant orconstricted portions as shown in Fig. 3 so that the grid when inposition partially encircles each of the anode rods 12 and I3 and thecathode II.

In tubes which Ihave constructed in accordance with my invention, I havefound that the distance d, Fig. 3, is quite important in determining theamplification constant of the tube and its other electricalcharacteristics. With the structure shown in the figures, a great manyof the electrons in their journey from the cathode I l to the anode rodsI2 and I3 must pass through the control grid l5 twice. That is, theypass through the grid from the cathode outward and from outside of thegrid inward to the anode rods l2 and 13. This weaving of the electronsthrough the grid causes a multiplication of the amplification factor andrenders possible the attainment of a high transconductance triode.

For example, when the distance d has a value of approximately 0.045inch, I obtain an amplification factor of 3, and when this constrictedportion is reduced only slightly, as for instance to 0.020 inch, Iobtain an amplication factor of 9. In tubes which I have constructedwith the distance d having a value of 0.025 inch, I have been able toduplicate the commercial triode Type 227 in an electrical manner eventhough the anode instead of having a large surface consists of only awire twenty-five thousandths of an inch in diameter. This will serve toillustrate the degree of simplification and economy attained.

Preferably the anodes are constructed of refractory material such astungsten, molybdenum or nickel, depending upon the number of watts ofenergy it is desired to dissipate. It is therefore essential that thespacers l1 and i8 be able to withstand this high temperature withoutcausing the evolution of gases as in the case of mica and for thisreason the mica spacer 20 is provided with the aperture as shown in Fig.4. Because of the fact that the grid is external with respect to theanode it can be-maintained at a sufiiciently low temperature to avoidprimary electron emission and at the same time the anodes may beoperated at a very high temperature in order to achieve the desireddissipation of energy. The anode rods may be maintained at a white heator just under a temperature at which the vapor pressure of the metal ofthe rod will not cause thinning out of the rod for several thousandhours. The energy therefore which is radiated from the anodes is in theform of light and from physical laws it follows that the energy perquantum increases with the increasing frequency of light. Consequently,the dissipation of energy from the'refractory anode rods takes placeefliciently within a frequency spectrum corresponding to white light,whereas in the case where a large area anode is utilized, the radiationtakes place in the red end of the spectrum in the form of long wavelength heat rays. Obviously, the structure is simple and economical dueto the small size of the anodes and as these anodes. with the externallydisposed grid can be operated at very high temperatures the equivalentdissipation of energy to that of the older type construction can beattained.

The ratio Fig. 3, is important in the functioning of the tube. I find byexperiment that it is not useful to have this ratio of greater valuethan 33%. The maximum utility is in the region when this variation isequal to less than When this factor is equal to some value of the orderof 10% then in the region of cut-off a low amplification factor isattained and at zero voltage on the grid a high amplification factor isattained. By proper design of the factor it is possible to design a tubewith a variable amplification factor to achieve valuable com mercialresults.

It is of advantage in my novel construction to provide an exteriormetallic coating 2| on the envelope and base 2, as the electronsemerging from the cathode through the control grid and weaving backagain through the grid cause a certain number of electrons to existoutside of the grid for a small period of time. If an uncoated envelopewere used, grid action of wall charges would produce undesirableeffects, but with the use of the coating 2| as shown this grid action ofwall charges is minimized and the fluctuation component due thereto isreduced to a minimum. Ordinarily this metallic coating 2| is grounded tothe cathode in order to prevent the above noted ill effects and alsostray field charges from affecting the fluctuation component of theanode current.

In Fig. 2, I have shown a modification of my invention in which therod-like anodes I2 and I3 are brought out to separate contact prongs as4 and I6 that the tube may be used as a double anode tube. The otherelements shown in Fig. 2 are exactly the same as those described withreference to Figs. 1, 3, and 4 and it is thought that no furtherexplanation of this embodiment is necessary.

From the foregoing it will be readily apparent that I have produced anovel thermionic tube in which, while the present desirable electricalcharacteristics are retained and new desirable features are attained,the construction is simplified and rendered more economical to produce.

It should be noted also that the energy radiation of the anode isincreased to provide fully effective energy dissipation and that amultiplication of the amplification factor may be easily achieved, orthat a variable amplification factor may be attained.

It should be further noted that the relatively large grid area and theexternal position of the grid permits maintaining the grid at atemperature sufficiently low to ensure substantially no primary electronemission. It should also be pointed out that the structure permits of aminimum direct capacitance between the anode and control grid, therebyproduces a tube which may be effectively used in the very short wavespectrum as an oscillator.

Having thus completely described and disclosed my invention, what Iclaim and desire to secure by United States Letters Patent is asfollows:

1. An electron discharge device comprising, a substantially evacuatedenvelope containing a cathode, an anode, said anode being in the form ofa plurality of rods electrically interconnected, and a control gridexternally disposed with relation to both said cathode and said anode,and formed with re-entrant portions located between said cathode andanode.

2. An electron discharge device comprising, a substantially evacuatedenvelope containing a cylindrical cathode, an anode, said anode being inthe form of a plurality of rods electrically interconnected and acontrol grid helically and externally disposed with relation to bothsaid anode and cathode and having constricted portions between saidcathode and anode whereby said cathode and anode are each partiallyencircled by said grid.

3. An electron discharge device comprising, a substantially evacuatedenvelope containing a cathode, a plurality of anodes and a control gridexternally disposed relative to said cathode and each of said anodes andhaving re-entrant portions located between said cathode and each of saidanodes.

4. An electron discharge device comprising, a substantially evacuatedenvelope containing a cathode, a pair of anodes positioned substantiallyco-planar with said cathode, and a control grid externally disposedrelative to said cathode and each of said anodes and having constrictedportions located between said cathode and each of said anodes wherebysaid cathode and each of said anodes are partially encircled by saidgrid.

5. An electron discharge device comprising a substantially evacuatedenvelope containing a cathode and an anode in the form of a rod of smalldiameter, a control grid. externally disposed relative to both saidcathode and anode and formed with re-entrant portions located betweensaid cathode and anode and a metallic coating on the exterior surface ofsaid envelope for co-action with the electrodes located within saidenvelope.

HENRY W. PARKER.

